Intraoperative assessment of stapes movement

A method is described that allows, for the first time, intraoperative vibra tion modes assessment of the acoustically stimulated stapes by means of sca nning laser Doppler interferometry (LDI). The study was designed to answer the following questions: 1) Is LDI practical for taking measurements during surgery? 2) Are the results comparable to the findings in temporal bone pr eparations? and 3) Do the vibration characteristics of the stapes change af ter the posterior incudal ligament is detached from the incus? Seven patien ts with profound bilateral hearing loss who were undergoing cochlear implan tation were included in the study. The measurement system was easily applic able for intraoperative measurements and allowed contact-free analysis with very high accuracy. No major differences in the results from the live huma n subjects and temporal bone preparations were observed. The stapes movemen t was predominantly pistonlike at the lower frequencies and became complex at higher frequencies. Sacrificing the posterior incudal ligament had no st atistically significant effect on stapes vibration.